Thoroughly grease a 9-by-11-inch pan and set aside.
Melt the butter in a large saucepan over medium-low heat. Add the marshmallows and salt and stir until melted. Halfway through the melting process, add the chocolate-hazelnut spread and stir until smooth.
Meanwhile, melt the semisweet chocolate over a double boiler until smooth. Remove from the heat and let it cool quite a bit.
Add the crisped rice cereal to a large bowl and fold in the marshmallow/chocolate-hazelnut mixture. When it's almost all combined, add the mini marshmallows and continue folding until everything's combined.
Immediately press the mixture into the prepared pan. Sprinkle with half the pecans. Drizzle the chocolate in zigzags all over the top of the treats. Sprinkle the remaining pecans on top. Allow to set, then cut into squares.